For stable operation of network services, it is required to detect causes of network failures. One of network failures is congestion of data. The congestion of data refers to a condition in which discarding of traffic, for example, takes place as a result of influx of a larger quantity of traffic than a quantity of traffic with which the network can treat. One method for detecting such congestion of data is to transmit a measurement packet such as Ping onto the network. Presence or absence of congestion of packets on the network is detected by transmitting a measurement packet to terminals and analyzing responses to the measurement packet, e.g., whether responses are sent back from the terminals or a response time from the terminals.
Japanese Patent Laid-Open No. 2007-208571 discusses a method for determining the presence/absence of congestion and/or the level of congestion, such as severe or mild congestion, based on the fact that packets are discarded when congestion has occurred. For example, the method analyzes the number of packet losses and/or the number of packet loss occurrences in segments with packet losses to determine the level of congestion.